1. Technical Field
The present disclosure relates to coupling a throttle body with an intake manifold.
2. Background Art
Automotive throttle bodies have a flange for coupling with a flange located on an inlet side of an intake manifold. Typically the throttle body is metallic, possibly of aluminum, with a metallic throttle plate pivoting inside. Modern intake manifolds are injection molded of a polymeric material. The coupling between the two are shown in FIG. 1. A cross-section of a portion of throttle body 10 is shown in FIG. 1. The throttle body has a throttle plate 11 that rotates about rod 13. Throttle plate 11 may be mechanically actuated by the operator of the vehicle. More commonly found recently, is an electronically actuated throttle plate that is actuated by a stepper motor (not shown) or other suitable motor. Throttle plate 11 includes a flange 14 that couples with a flange 16 of an intake manifold (a portion of a cross-section of which is also shown in FIG. 1). Unthreaded through holes 18 are provided on flange 14. At least three through holes are provided in flange 14. However, the cross-section represented in FIG. 1 is taken through only two through holes 18. Flange 16 of intake manifold 12 includes threaded inserts 20. Although not shown in FIG. 1, a bolt is provided for each pair of through hole 18 and threaded insert 20 and is inserted in the direction of arrow 22.
To allow for coupling of the two parts in spite of manufacturing tolerances and to allow the bolts to be easily inserted, through holes 18 are slightly oversized. The inside diameters of throttle body 10 and intake manifold 12 may be offset slightly due to the slight oversize of the inside diameters of throttle body 10 and other manufacturing tolerances. The mismatch is shown in FIG. 1 as “m.” As flow travels from throttle body 10 into intake manifold 12, the mismatch on the top side of the joint is called a rearward facing step and the mismatch on the lower side of the joint is a forward facing step. The mismatch leads to eddies being formed and leads to a whistling sound that is noticeable to the operator of the vehicle. Such a mismatch also slightly negatively impacts the maximum amount of flow to the engine, i.e., slightly hurting peak engine performance. The mismatch shown in FIG. 1 is particularly troublesome because it is located proximate the flow when throttle valve 11 is partially open. That is the substantially round throttle plate and the substantially round duct of throttle body 12, seal around the periphery when throttle valve 11 is in a vertical position. As throttle valve 11 is partially opened, flow rushes through the crescent-shaped openings at uncovered by throttle valve 11. Thus, a mismatch occurring in the vicinity of where the majority of the flow enters is particularly troublesome.